Insulating and shielding enclosure



YNov. 22, 1960 E. D. BURNS 2,961,478

INSULATING AND SHIELDING ENCLOSURE Filed OOL. 10. 1957 vtm INV ENTOR. E VERE TT D. BURNS BY JKM/y ,422

HIS ATTORNEY INSULATING AND SHIELDIN G ENCLOSURE Everett D. Burns, Wenham, Mass., assignor to McMillan Industrial Corporation, a corporation of Massachusetts Filed Oct. 10, 1957, Ser. No. 689,299

9 Claims. (Cl. 174-35) My invention relates to an insulated enclosure and to construction details of such an enclosure.

More particularly, my invention relates to an enclosure oi the type exemplified by the so-called freespace rooms, which are often used as a site for the testing of radio and microwave equipment or for the making of delicate measurements which necessitate the exclusion of all stray radio-frequency and microwave energy.

Still more particularly, my invention relates to an enclosure, and construction details of such an enclosure which, as a consequence of its insulated walls, may be adapted for purposes such as refrigerated storage or for a number of other purposes where isolation either as to temperature, radio-frequency energy or microwave energy is important.

ln the past, shielded rooms have been constructed and employed for the accommodation of delicate measurements and electrical tests. One purpose of such rooms, in which apparatus such as antennas is undergoing tests,

is to simulate free space in that, if the walls of the room absorb all energy which strikes them rather than reflecting such energy, the test results obtained from the apparatus are the same as the results would be if the apparatus were tested in free space, infinitely far from solid objects of all types. In addition to rooms capable of absorbing microwave energy which strikes their walls, rooms have been provided which are sheathed with conductive sheets capable of preventing passage therethrough of radio-frequency energy. Thus by cornbining the effects of the microwave-energy-absorptive material and the conductive sheeting, a high degree of isolation from stray electromagnetic energy can be achieved.

In the past, some attempt has been made to combine shielding of electromagnetic energy, as described above, with thermal shielding. Rooms have been constructed with absorbing material on their inner walls and conductive sheeting on their outer walls, and with thermalinsulating structural material constituting the walls themselves. In order to get a high degree of thermal insulation, it has generally been necessary to use multiple layers of structural material with the joints between panels of such material staggered in order to minimize leakage of air therethrough. Such construction methods have resulted in chambers which were unnecessarily bulky, expensive, hard to assemble, and which were in most cases not completely air-tight.

ln view of the deficiencies of prior-art construction methods, it is an object of my invention to make an insulated enclosure which is cheap, light, simple, permanent, and easy to assemble.

It is another object of my invention to make an insulated enclosure which is substantially air-tight and which is capable of preventing the passage of substantially all electromagnetic energy either of radio frequencies or of microwave frequencies.

It is further object of my inventionhtomake an tates Patent C) 2,961,478 Patented Nov. 22, 1960 insulated enclosure which may not only be easily assembled but which may also be disassembled and carried to a distant point for re-assembly.

Briefly, I have fulfilled these and other objects of my invention by building up an enclosure having walls of expanded plastic foam fastened together with keys of a laminated conguration, such keys having a cross-section which is tapered toward its ends and fitting into slots in the panels of said walls to retain the panels in position by means of a Wedging action of the keys. Such walls may be constructed of a single layer of expanded plastic` foam, while the keys should preferably be laminated with a central core of elastic material and outer layers of some material such as an expanded plastic foam having higher strength than the foam employed in the walls of the enclosure. Such walls may be lined with material for absorbing microwave energy and may be covered with conductive sheeting to prevent the passage of radio-frequency energy, the joints in the sheeting being sealed in such a way as to make them air-tight and radiation-proof.

For a full understanding of my invention, reference should now be made to the following detailed specification taken in conjunction with the associated drawings, in which:

Figure l is a perspective View of the components which may tit together to form a corner assembly of an insulated enclosure according to my invention;

Figure 2 is a sectional view of a key according to my invention, showing the key in place and joining together two adjacent panels of the wall, which are in turn covered on one side with microwave-energy-absorbing material and on the other side with radio-frequencyenergy-sliielding material; and

Figure 3 is a sectional view of an alternative configuration of wall joint in which a plurality of keys are employed and supplementary measures have been taken to prevent leakage of air through the joint.

Turning to Figure 1 of the drawings, which shows the components of a corner assembly ready to be moved together to complete such an assembly, it will be noted that walls and ceiling members are shown and that the keys permitting juncture of such walls and ceiling appear clearly in perspective view. Such a use of keys is one of the more sophisticated uses of such keys. A more elementary key joint, and one which should preferably be discussed first, is shown in Figure 2, wherein wall panels 11 and 12 meet at an interface 13 to form a butt joint. As has been previously mentioned, wall panels 11 and 12 may be of an expanded plastic foam such as Styrofoam brand of expanded polystyrene as manufactured by the Dow Chemical Company. Typical suitable designations of Styrofoam for this use are HD1, No. 22 and No. 33. It will be understood that, while Styrofoam is a preferred material for the wall panels according to my invention, other plastic foams, preferably unicellular in nature, may be employed. It will be noted that panel 11 has a tapered slot 16 in its edge, while panel 12 has a tapered slot 17 in its corresponding edge, both slots being employed to receive the key generally designated at 20. Slots such as those at 16 and 17 may generally be milled in the edges of the wall panels, but may be routed by hand near the corners of the panels in order to prevent damage thereto.

Key 20 should preferably have at least three layers such as those shown at 22, 23, and 24, in which layer 23 should be elastic, while layers 22 and 24 should have cross-sections which taper toward their ends. I prefer to make my central layer 23 of some material such as rubber, either solid or foam, neoprene, cork, or suitable plastic. While I prefer to employ an elastomeric material, it is possible to use a plastic such as a vinyl or a polyurethane providing sutiiciently elasticity can be achieved. I prefer to form layers 22 and 24 of a foam such as high-strength Styrofoam designated HD2. The layers of key 20 should be fastenedV together, preferably with a eXible adhesive such as 'those having a rubber base. A water-emulsied rubber-base adhesive or an adhesive of rubber dissolved in an aliphatic hydrocarbon may be employed so long as the hydrocarbon is not such as to damage any of the struc-V tural materials of the key.

It will be noted that layers 22 and 24 are tapered and that layers 22, 23, and 24 completely fill slots 16 and 17. I prefer that the relaxed cross-section of the key according to `my invention be slightly larger than the crosssection of Vthe corresponding slots in the wall panels, in order that when the keys are forced into the slots, central layer 23 of each key is compressed, thereby making a veryeffectiveseal. it will benoted that, if key 20 were driven into slot 16 of panel 1l, one end of layer 23 would be compressed more than the other. Then, when panel 12. is brought into place with key 20 in slot 17, the other endof key 2t) is likewise compressed, resulting in a symmetrical cross-section of layer 23 and of the key. i In -Figure 2 is shown a surface 26 Vof conductive sheeting on one side of the wall and a lining 28 of microwaveenergy-absorbing material on the other side of the wall. As has been explained in the preceding paragraphs, sheeting 26 serves to prevent .the passage of radio-frequency energy, while material 28 serves to absorb microwave energy .which strikes it. While the layers of key 2t! should be fastened .together with a llexible adhesive, sheeting 26 ay be fastened to the wall panels with an adhesive which need not be flexible, such as an epoxy adhesive represented by Epon VI, a product of Shell Chemical Corporation. It will be understood that, while for the purposes of a shielded free-space room sheeting 26 should be of metal, an enclosure used for other purposes might have some non-conductive sheeting such as liberboard on its outer surface. Once again, the fiberboardmight be fastened to the wall panels with a suitable nonflexible adhesive.

Microwave-absorbing material 28 might typically comprise an impedance-matching layer 30 in which ogival holes such as at 32 have been formed. The surfaces of holes 32 are covered with a material which is lossy and which .dissipates `any microwave energy which impinges upon it Vwhile reflecting a minimum of such energy. A .microwave-absorbing material of this type is manufactured by McMillan Laboratory, Incorporated, Ipswich, Massachusetts, and may be fastened to the wall panels with any suitable adhesive.

If the enclosures according to my invention is to be employed in maintaining the separation between air masses of widely divergent temperatures, the efficiency of such an lenclosure may be maximized by making the walls rather thick, e.g., of the order of one foot, and by employing a plurality of keys in each joint between adjacent panels. Such a configuration is shown in Figure 3, wherein adjacent panels 35 and 36 are joined together by keys depicted generally at 38 and 39. Once again, keys of the tapered-cross-section 3-lamination type are shown, although it will be understood that keys having in excess of three laminations might be employed. In order to make the joint between panels 35 and 36 as gas-tight as possible, `a grease seal is shown at 41, and the outer edges of the butt joint are shown covered by tapes at @i3 vand 454. A metallic strip is shown at 46 which serves the dual purpose of retaining tape 43 in place and of augmenting the tightness of the electrical seal. Tapes 43 and 44 might be of rubber, plastic, or silicone, while metal strip i6 might be of the same metal as the conductive sheeting S on the surface of panels 35 and 36. Metal strip 46 might be fastened to conductive sheeting 4S by means of sheet-metal screws or nylon-locking screws, and might be of galvanized steel or copper or brass in order to secure a high degree of conductivity.

In View of the thermal conductivity of screws, it is preferable that they not extend very far into the plastic foam of the wall panels. If radio-frequency energy is to be effectively screened, there should be a multi-contact metal strip between strip 46 and conductive sheeting 48, thus assuring the freedom of currents to flow between all portions of the sheeting. I. prefer to employ Phosphor bronze or beryllium-copper alloy as the material for the multi-contact metal strip.

Turning to Figure l, a corner assembly is shown which .might be representative of the corner of an enclosure either for refrigeration or electrical test purposes. While it will be understood'that wall 6l and wall 62 are joined to each other and to a ceiling 63 respectively by a vertical key 65 and a horizontal key 66, each wall is assumed to be formed of panels such as those which have been described in the discussion of Figures 2 and 3 and which are similarly joined together by keys of the types described in connection with those figures. In wall 61 is shown a slot 67 which receives vertical key 65, and there isa corresponding slot in wall 6l for the purpose of receiving horizontal key 66. The respective ends of keys 65 and 66 may be mitered in order to give satisfactory Contact between the two keys. Taking key 66 as an eX- ample of key structure, layer 70 represents the central elastic layer, while layers 71 and 72 represent the outer tapered layers.

The panel of wall 62 which is shown in Figure l is a special corner panel in which a slot is formed which is capable of receiving a special corner key 80. Corner key may have components 31 and 82 which are joined together by means of an adhesive at their corner. A vertical slot in the edge of wall 62, not shown, receives vertical key 65. When walls 61 and 62 have been joined together, ceiling portion 63, having slots and 86 milled therein, may be lowered over the tops of the walls to mate with the upper edges of keys 6 6 and 30. Ceiling portion 63 may be of expanded plastic foam, and like the wall portions, may have a conductive surface coating and a lining of microwave-energy-absorbing material. If the enclosure is to'be comparatively small, ceiling portion 63 may be self-supporting without the aid of additional structural members. On the other hand, if the room is to be very large, the wall and celing members may be assembled within a metal frame which lends to them the strength which is requisite for the support of the ceiling.

While the free-space room which has been described in the foregoing paragraphs is designed primarily for indoor use, it is entirely feasible to operate a free-'space room outdoors if the metal sheeting is perfectly watertight or if other means are provided for protecting the room from precipitation. If the room is operated indoors, the outer surfaces of the walls will presumably be at room temperature, while the temperature within the free-space room will be adjusted to any desired level, either above or below room temperature. If the freespace room is located outdoors, it may well be desired to maintain the interior thereof at room temperature despite variations in the temperature of the air outside the room. In either case, if heating, cooling, or airconditioning equipment is employed with the room, it will be desirable to shield any ducts that may be employed, in order that no undesirable electrical effects may be produced thereby. It may also be desirable to provide shielding material, yboth of the conductive-sheet type and of the microwave-energy-absorbing type to cover the door of the room.

While the foregoing description has been villustrated in terms of a free-space room for electrical measurements and test work, it should be emphasized that the principles for joining together wall panels by means of the key which I have devisedare equally applicable to refrigerators or to storage rooms such as those which are employed to maintain apples at a depressed temperature. .It may be seen that'I have r'ullled the objects of my invention by devising an insulated enclosure which is light, substantially air-tight, and which is capable of being assembled and disassembled at will. While certain embodiments of my invention have been described in the foregoing specification and shown in the drawings, 1 intend to have the scope of my invention limited only by the following claims.

I claim:

1. An insulated enclosure having walls of which the primary insulating constituent is expanded plastic foam, said foam being in the form of panels connected together to constitute said walls of said enclosure, said panels having slots in their respective edges and being connected together by means of keys of laminated structure tting into said slots in adjacent ones of said panels, said keys comprising at least three laminations of which an interior lamination is perceptibly elastic, and all of said laminations of said respective keys extending into said slots of said respective adjacent panels.

2. An insulated enclosure according to claim 1, in which said expanded plastic foam is expanded polystyrene.

3. An insulated enclosure according to claim 1, in which said keys have exterior laminations comprising expanded plastic foam characterized by strength greater than that of the expanded plastic foarn of said panels.

4. An insulated enclosure according to claim 1, in which said keys have a cross section which tapers from its central portion toward the end portions of said cross section.

5. An insulated enclosure according to claim 1, in which one surface of said walls is substantially covered with microwave-energy-absorbing material.

6. An insulated enclosure according to claim 1, in which connections between each adjacent pair of panels of said walls include a plurality of said laminated keys.

7. An insulated enclosure according to claim 1, in which said enclosure includes a ceiling and in which c011- nections between said walls and said ceiling, as well as between said panels of said walls, are made by means of laminated keys.

8. An insulated enclosure according to claim 1, in which one surface of said walls is substantially covered with a plurality of conductive sheets, and in which the joints between adjacent ones of said conductive sheets are covered by conductive strips.

9. A key adapted for insertion into slots in the edges of respective ones of a plurality of panels to be connected by said key, said key having a cross section which tapers evenly from the central portion thereof to the ends thereof, said key comprising at least three laminations of which an interior lamination is perceptibly elastic and a pair of exterior laminations comprise expanded plastic foam, all of said interior and exterior laminations extending to both ends of said cross section of said key, for insertion into said slots in said panels.

References Cited in the le of this patent UNITED STATES PATENTS 1,723,306 Sipe Aug. 6, 1929 1,913,290 Rockwell June 6, 1933 2,193,306 Tinnerman Mar. 12, 1940 2,229,279 Cranston et al J an. 21, 1941 2,405,987 Arnold Aug. 20, 1946 2,552,641 Morrison May 15, 1951 2,594,971 Moullin Apr. 29, 1952 2,599,944 Salisbury June 10, 1952 OTHER REFERENCES Publication I: Expanding Fields for Expanded Plastics (Breskin), published in Scientific American, September 1947 (pages 119-121 relied on). 

